Prof. J.P.N. Mishra
Blood was mixed suitably with an anticoagulant (Sodium citrate) and allowed to stand vertically in a special tube (Westergren tube), the erythrocyte has higher specific gravity than plasma, so it settle down, leaving a clear supernatant plasma above.
The length of the column of this clear supernatant plasma in millimeter (mm) after the end of first hour is the erythrocyte sedimentation rate (ESR).
